So there are a couple of ways to do this. I think the easiest is to use the "hide" option (this "hides" data from the view, but running sum will still have access to all weeks.
I the attached I created a dimension to mark TRUE the last 4 weeks
NB As I have an extra dimension in my view I need to alter the running sum, to just run over this
I can then "Hide" the False weeks...
Hope that helps and makes sense
Running Sum Restrict View.twbx 592.6 KB
Thanks Simon for helping me solving my questions in such a short time!